The present invention relates to a digital watermark insertion system that converts information into a digital watermark and then inserts it in an image.
Conventionally, this type of digital watermark insertion system is disclosed, for example, in JP-A-No. 191394/1997 or the literature, xe2x80x9cIEEE TRANSACTIONS ON IMAGE PROCESSINGxe2x80x9d, VOL. IP-6, No. 12, 1997, pp 1673-1687 and is designed to embed copyright information in digital signals creating audio and images.
FIG. 10 shows a conventional digital watermark inserter disclosed in the above-mentioned references. This inserter implements a DCT (Discrete Cosine Transform) or DFT (Discrete Fourier Transform) to input images and then outputs a transform coefficient to the mark inserter 1001. The mark inserter 1001 inserts a digital watermark signal in the transform coefficient output from the frequency converter 1000, with the digital watermark strength to be input. The inverse frequency converter 1002 subjects the watermarked transfer coefficient from the mark inserter 1001 to the inverse conversion opposite to the conversion by the frequency converter 1000 and then creates a watermarked image.
In operation, the frequency converter 1000 subjects all input images to the DCT or DFT process and then outputs the resultant transfer coefficients to the mark inserter 1001. The mark inserter 1000 also selects N transfer coefficients with the same digital watermark length in the transfer coefficient decreasing order and inserts a digital watermark in them. Specifically, a digital watermark is inserted according to the following formulas:
vxe2x80x2=v+xcex1xxe2x80x83xe2x80x83(formula 1)
or
vxe2x80x2=v(1+xcex1x)xe2x80x83xe2x80x83(formula 2)
where x represents a digital watermark signal; xcexd represents an embedded transfer coefficient; xcex1 represents a digital watermark strength; and xcexdxe2x80x2 represents a watermarked transfer coefficient.
The inverse frequency conversion circuit 1002 subjects the resultant watermarked coefficient to the inverse DCT or inverse DFT process and then creates a watermarked image.
The image-quality degradation of a watermarked image and a digital watermark resistance against attacking are in a tradeoff relationship. Both the factors are balanced by adjusting the digital watermark strength xcex1 input to the mark inserter 1001. As xcex1 increases, the image-quality degradation of a watermarked image becomes large but the attack resistance property increases. On the contrary, as xcex1 decreases, the image-quality degradation of a watermarked image can be suppressed but the attack resistance property decreases.
However, the above-mentioned digital watermark insertion system has the disadvantage in that it is difficult to properly set the digital watermark strength.
The difficulty comes from the fact that a user inconsiderately adjusts the digital watermark strength to insert a digital watermark. The conventional digital watermark insertion system does not include means for recognizing either how degree a possible image-quality degradation caused by digital watermark insertion is or how degree the resistant property against attacking is. Hence, the user can decide an optimum digital watermark strength only after the image-quality degradation caused by digital watermark insertion has been actually tried over plural digital watermark strengths. If the user does not try attacking, the attack resistance cannot be accurately evaluated.
A proper digital watermark strength greatly depends on the content of an image. Hence, the problem is that even if the relationships between digital watermark strength, image-quality degradation and resistant property against attacking are decisively shown to the user, it is difficult to apply the relationships to all images so that the resultant strength is different from the truly optimum digital watermark strength.
The present invention is made to solve the above-mentioned problems.
The objective of the invention is to provide a digital watermark insertion system that can automatically decide digital watermark strengths based on constraints and image features by a user.
Moreover, another objective of the present invention is to provide a digital-watermark-characteristic table creating device that can automatically decide digital watermark strengths based on constraints and image features by a user.
The objective of the present invention is achieved by a digital watermark insertion system, wherein digital watermark information is inserted in an image, comprising means for calculating feature values of input images, classifying the input images into categories with the feature values, and outputting a category index; storage means for storing digital watermark characteristic tables according to predetermined various category indexes, each of the tables describing relationships between digital watermark strength, image-quality degradation degree and attack-resistant evaluation value, selecting a digital watermark characteristic table according to the category index of an input image, and outputting an image-quality degradation degree corresponding to an input digital watermark strength and an attack-resistant evaluation value; digital-watermark-strength calculation means for outputting the digital watermark strength to the storage means, and deciding and outputting an optimum digital watermark strength using digital-watermark-strength constraint information to be input based on the image-quality degradation degree and the attack-resistant evaluation value output from the storage means; and means for converting embedded data to be input into a digital watermark, inserting the digital watermark into the input image, with the optimum digital watermark strength acting as an input parameter, and outputting it as a watermarked image.
In the digital watermark insertion system according to the present invention, the digital-watermark-strength constraint information is a permissible critical value of an image-quality degradation degree. The digital-watermark-strength calculation means decides an optimum digital watermark strength within a range over which an image-quality degradation degree is less than the permissible critical value of the image-quality degradation value.
In the digital watermark insertion system according to the present invention, the digital-watermark-strength constraint information is a critical value of a safety index to attack. The digital-watermark-strength calculation means decides an optimum digital watermark strength within a range where an attack resistant evaluation value is more than the safety index critical value.
In the digital watermark insertion device according to the present invention, the digital-watermark-strength constraint information is a weighting index deciding a balance between an image-quality degradation degree and a safety index. The digital-watermark-strength calculation means decides a contribution ratio by the weighting index, the contribution ratio at which the image-quality degradation degree and the safety index contributes to decide an optimum digital watermark strength.
According to the present invention, the digital watermark insertion system further comprises digital-watermark-characteristic table creation means for creating a digital watermark characteristic table describing relationships between digital watermark strength, image-quality degradation degree and attack-resistant evaluation value and for inputting a created digital watermark characteristic table to the storage means.
Moreover, according to the present invention, the digital watermark insertion system, wherein the characteristic table creation means, comprises digital watermark insertion means for converting embedded information to be input into a digital watermark, and inserting the digital watermark into an input image, with a digital watermark strength to be input, whereby a watermarked image is created; attacked-image creation means for attacking the watermarked image with an attack strength, according to an attack parameter to be input, and then creating an attacked-image; digital watermark detection means for detecting on trial the digital watermark of the attacked image and then outputting a detection result; image-quality calculation means for comparing the input image with the watermarked image, calculates the degree of image-quality degradation caused by digital watermark insertion, and then outputting the calculation result as an image-quality degradation amount; image categorizing means for calculating a feature amount of the input image, classifying the input image into a category with the resultant feature amount, and outputting an category index; and characteristic table creation means for obtaining a detection ratio by totaling a series of detection results detected to combinations of various input images and various digital watermark strengths, by category index, digital watermark strength and attack parameter; for obtaining an image-quality,amount by calculating attack-resistant evaluation values from the detection ratio by category index and digital watermark strength and by averaging the image-quality degradation amounts by category index and digital watermark strength; and creating a digital watermark characteristic table showing corresponding relationships between digital watermark strength, the image-quality degradation degree and the attack-resistant evaluation value by category index.
In the digital watermark insertion system according to the present invention, the characteristic table creation means comprises means for totaling digital watermark detection results by attack parameter, digital watermark strength and category index and then outputting detection ratio data; means for averaging image-quality degradation amounts by category index and digital watermark strength and then for outputting an image-quality degradation degree; means for obtaining the relationship between attack parameter and detection ratio based on an attack parameter and the detection ratio data and then calculating an resistant evaluation value; and means for integrating digital watermark strength, the image-quality degradation degree and the resistant evaluation value and then creating a digital watermark characteristic table.
In the digital watermark insertion system according to the present invention, the resistant evaluation value calculation means calculates a resistant evaluation value by obtaining an inner product of a function representing the change of a detection ratio for an attack parameter and a weighting function.
In the digital watermark insertion system according to the present invention, the resistant evaluation value calculation means obtains an attack parameter range from a function representing the change of a detection ratio for an attack parameter, the attack parameter range over which the detection ratio is more than a threshold value, and decides a resistant evaluation value based on the length of the attack parameter range.
Furthermore, according to the present invention, a digital watermark characteristic table creating device, comprises digital watermark insertion means for converting embedded information to be input to a digital watermark, and inserting the digital watermark into an input image, with a strength corresponding to a digital watermark strength, whereby a watermarked image is created; attacked image creation means for attacking the watermarked image with an adjusted attack strength according to an input attack parameter, and then creating an attacked image; digital watermark detection means for detecting on trial the digital watermark of the attacked image and then outputting the detection result; image-quality degradation calculation means for comparing the input image with the watermarked image, calculating the degree of image-quality degradation caused by digital watermark insertion, and then outputting the calculation result as an image-quality degradation amount; image categorizing means for calculating a feature amount of the input image, classifying the input image into a category with the resultant feature amount, and then outputting an category index; and characteristic table creation means for obtaining a detection ratio by totaling a series of detection results detected to combinations of various input images and various digital watermark strengths, by category index, digital watermark strength and attack parameter; for obtaining an image-quality degree by calculating attack-resistant evaluation values from the detection ratio by category index and digital watermark strength and by averaging the image-quality degradation amount by category index and digital watermark strength; and then creating a digital watermark characteristic table showing corresponding relationships between digital watermark strength, the image-quality degradation degree and the attack-resistant evaluation value by category index.
In the digital watermark characteristic table creating device according to the present invention, the digital watermark characteristic creation means comprises means for totaling digital watermark detection results by attack parameter, digital watermark strength and category index and then outputting detection ratio data; means for averaging image-quality degradation amounts by category index and digital watermark strength and then outputting an image-quality degradation degree; means for obtaining the relationships between attack parameters and detection ratios based on an attack parameter and the detection ratio data and then calculating a resistant evaluation value; and means for integrating digital watermark strength, the image-quality degradation degree and the resistant evaluation value and then creating a digital watermark characteristic table.
In the digital watermark characteristic table creating device according to the present invention, the resistant evaluation value calculation means calculates a resistant evaluation value by obtaining an inner product of a function representing the change of a detection ratio for an attack parameter and a weighting function.
In the digital watermark characteristic table inserting device according to the present invention, the resistant evaluation value calculation means obtains an attack parameter range from a function representing the change of a detection ratio for an attack parameter, the attack parameter range over which the detection ratio is more than a threshold value, and decides a resistant evaluation value based on the length of the attack parameter range.
According to the present invention, a computer-readable recording medium, wherein the medium records a program realizing a digital watermark insertion system, which inserts digital watermark information into an image, on a computer, comprises means for calculating feature amounts of an input image to classify the input image into a category with the calculated feature amounts, and outputting an category index; storage means for previously storing a digital watermark characteristic table describing the relationships between digital watermark strength, image-quality degradation degree and attack-resistant evaluation value by various category indexes, for selecting the digital watermark characteristic table according to the category index of the input image, and for outputting both the image-quality degradation degree corresponding to an input digital watermark strength and an attack resistant evaluation value; and means for outputting the digital watermark strength to the storage means, deciding an optimum digital watermark strength according to the image-quality degradation degree and the resistant evaluation value output from the storage means, based on input digital watermark strength constraint information, converting embedded data into a digital watermark, and then inserting the digital watermark in the input image, with the optimum digital watermark strength acting as an input parameter, and then outputting the resultant data as a watermarked image.
According to the present invention, the computer-readable recording medium further comprises digital-watermark-characteristic table creation means for creating a digital watermark characteristic table describing relationships between digital watermark strength, image-quality degradation degree and attack-resistant evaluation value and for inputting a created digital watermark characteristic table to the storage means.
Moreover, according to the present invention, a computer-readable recording medium, wherein the medium records a program realizing a digital-watermark-characteristic table creation device on a computer, comprises digital watermark insertion means for converting embedded information to be input into a digital watermark, inserting the electric watermark into an input image, with a strength corresponding to an input digital watermark strength, and creating a watermarked image; attack image creation means for adjusting the attack strength of the watermarked image according to an input attack parameter, and creating an attacked image; digital watermark detection means for detecting on trial the digital watermark of the attacked image and then outputting a detection result; image-quality degradation calculation means for comparing the input image with the watermarked image, calculating a degree of image-quality degradation caused by digital watermark insertion, and outputting the calculation result as image-quality degradation amount; image categorizing means for calculating feature amounts of the input image, classifying the input image into a category with the feature amounts, and outputting an category index; and characteristic table creation means for obtaining a detection ratio by totaling a series of detection results detected to combinations of various input images and various digital watermark strengths, by category index, digital watermark strength and attack parameter; for obtaining an image-quality amount by calculating attack-resistant evaluation values from the detection ratio by category index and digital watermark strength and by averaging the image-quality degradation amount by category index and digital watermark strength; and creating a digital watermark characteristic table showing corresponding relationships between digital watermark strength, the image-quality degradation degree and the attack-resistant evaluation value by category index.